The present invention relates to an improved form of gravity separator for mixtures of immiscible liquids of different densities, such as, for example, oil and water.
More specifically, the invention is an improved gravitational separator of the type utilizing a collection tank or housing for receiving a mixture of the fluids to be gravitationally separated, the tank having a reaction member preferably in the form of either a floating dome or diaphragm element within the upper area of the tank which serves as a reaction surface against which the volume of lighter (less dense) fluid accumulated within the upper portion of the tank exerts an upward, buoyant influence.
Separators of the type utilizing a floating dome are known in the prior art, as exemplified in the British Patent Specification No. 1,212,553 to Cornelis in'tVeld published Nov. 18, 1970 and U.S. Pat. No. 3,628,660, also to in'tVeld, granted Dec. 21, 1971. In separators of this type, the mixture of lighter and heavier fluids (oil and water, generally) is admitted to the interior of the separator beneath the dome under positive pressure or is inducted therein by suction of the heavier fluid from the heavier fluid discharge pipe of the separator, with the separator being hermetically sealed. The mixture of heavier and lighter fluids gravitationally separates in the separator, with lighter fluid rising up under the dome and heavier fluid sinking to the lower part of the separator vessel beneath the dome.
The gradual accumulation of lighter fluid beneath the dome, which is counterbalanced so as to normally be slightly negatively buoyant in the heavier fluid, causes the dome to float upwardly in the heavier fluid within the separator. It is customary to sense the high limit position of the dome to produce a control signal useful to instigate valve and pump actuations which enable the removal of less dense separated fluid from beneath the dome.
Gravitational separators of this type that are used to separate oil from an oily water mixture are provided with filter or coalescer screens or elements between the lower part of the separator and the water discharge pipe to collect any lingering droplets of oil carried to the lower part of the separator. Such screens are backwashed periodically to remove the oil clinging to the coalescers and, as described in the above-referenced U.S. Pat. No. 3,628,660, such backwashing of the screens can be carried out quite efficiently during the oil discharge mode of separator operation. That is, it is customary procedure to remove the accumulated oil from beneath the floating dome by pressurizing the clean water discharge pipe of the separator to admit clean water backwards into the lower end of the separator through the coalescer screens, and into the area beneath the dome to thereby force accumulated oil out of the separator under positive pressure. Only the discharge of oil is desired, of course, and the reverse inflow of water is ceased when the accumulated oil has been discharged and the dome has sunk to its lower starting level.
Several problem areas have been encountered with the use of separators of the type just described. There has arisen, for example, a need for a simple, efficient and substantially fail-safe system to precisely counterbalance the floating dome or the diaphragm beneath which the separated oil is trapped and to accurately sense when the volume of separated oil has reached an upper limit within the separator so that removal procedures can be instigated. Such a system is disclosed and claimed in my co-pending application identified above. Also, the flow pattern of water through the coalescer screens has been found to be less than ideal both in forward and reverse flush senses. Ideally, the flow pattern in a forward direction through the coalescer screens should be uniform across all of the screens in the coalescer system and, when the screens are backflushed, the backflush flow pattern should occur entirely across the surfaces of the coalescer screens to remove oil droplets therefrom. Furthermore, the discharge of oil from between the coalescer screens should be as complete as possible during the backflush operation. Finally, it has been found to be highly desirable to prevent any accumulation of oil above the separator reaction member during the operating life of the separator, since accumulation of the less dense fluid above the member causes an inaccurate flotation response of the member to the accumulated oil beneath the dome.
Another approach to the reaction member counterbalance problem has been described in U.S. Pat. No. 3,957,638 granted May 18, 1976, and assigned to the assignee of the instant application. The description of that prior art system is incorporated herein by reference.
The present invention finds particular application in a bilge water disposal system for a vessel, such as described in U.S. Pat. No. 4,018,683, co-owned by the assignee of the present invention, and which is also intended to be incorporated herein by reference. Other applications of the present invention, of course, are envisioned in industrial installations ashore for separating mixtures of immiscible fluids of different densities.